This invention relates to a recording and/or reproduction apparatus and a recording and/or reproduction method, and more particularly to a recording and/or reproduction apparatus and a recording and/or reproduction method wherein focusing control can be performed rapidly and with certainty upon an optical disk having two or more record layers.
An optical disk as represented by a compact disk has only one information record layer. In recent years, it is demanded to increase the recording capacity. Such increase in capacity can be achieved, for example, by decreasing the track pitch or by reducing the pit size. Also an optical disk of a different type has been proposed wherein it has a plurality of record layers formed therein in order to further increase the capacity.
FIG. 21 shows an exemplary construction of an optical disk of the type just mentioned. Referring to FIG. 21, in the optical disk shown, a record layer A is formed on a disk base plate 101, and another record layer B is formed on the record layer A. A protective film 102 is formed on the record layer B.
The disk base plate 101 is made of a transparent material such as, for example, polycarbonate. The record layer A is formed from a translucent film while the record layer B is formed from a total reflection film of, for example, aluminum or a like metal.
In order to reproduce information from the record layer A, a laser beam is focused on the record layer A as denoted by reference character L.sub.1, and reflected light from the record layer A is detected.
On the other hand, in order to reproduce information recorded on the record layer B, a laser beam is focused upon the record layer B through the record layer A formed from a translucent film as denoted by reference character L.sub.2. Then, reflected light from the record layer B is received through the record layer A and detected. In this manner, since the record layer A is formed from a translucent film, information of the record layer B can be read through the record layer A.
In order to change, while a laser beam is focused upon the record layer A (or the record layer B), the record layer as an object of reproduction to the record layer B (or the record layer A), jump pulses should be applied to a focusing servo loop to cause the optical head to jump toward the new record layer and then focusing servo should be applied so that the focusing error signal may be minimized on the new record layer.
However, the position at which the focusing error signal exhibits a minimum value is not necessarily an accurate focus position because of a dispersion of the optical head or the disk in production or from some other cause. Therefore, normally an offset signal is added to the focusing error signal so that an optimum focusing condition can be obtained.
However, in the related art apparatus, the offset value is fixed irrespective of from which one of record layers information is reproduced. Accordingly, the related art apparatus has a subject to be solved in that it is difficult to reproduce information stably from a plurality of record layers.